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A101729 Indices of primes in sequence defined by A(0) = 41, A(n) = 10*A(n-1) + 51 for n > 0. 1
0, 1, 6, 8, 13, 23, 44, 48, 72, 73, 231, 337, 396, 503, 1062, 2816, 5304, 16767, 27059 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Numbers n such that (420*10^n - 51)/9 is prime.

Numbers n such that digit 4 followed by n >= 0 occurrences of digit 6 followed by digit 1 is prime.

Numbers corresponding to terms <= 503 are certified primes.

a(20) > 10^5. - Robert Price, May 27 2015

REFERENCES

Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.

LINKS

Table of n, a(n) for n=1..19.

Makoto Kamada, Prime numbers of the form 466...661.

Index entries for primes involving repunits.

FORMULA

a(n) = A102994(n) - 1.

EXAMPLE

461 is prime, hence 1 is a term.

MATHEMATICA

Select[Range[0, 1000], PrimeQ[(420*10^# - 51)/9] &] (* Robert Price, May 27 2015 *)

PROG

(PARI) a=41; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+51)

(PARI) for(n=0, 1500, if(isprime((420*10^n-51)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A102994.

Sequence in context: A058938 A315877 A315878 * A209686 A283286 A283375

Adjacent sequences:  A101726 A101727 A101728 * A101730 A101731 A101732

KEYWORD

nonn,hard,more

AUTHOR

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004

EXTENSIONS

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

a(18)-a(19) from Kamada data by Ray Chandler, Apr 30 2015

STATUS

approved

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Last modified May 19 14:45 EDT 2019. Contains 323395 sequences. (Running on oeis4.)